ABSTRACT
The safety of reinforced concrete bridges is strongly affected by many deterioration factors. The most important factor is reinforcement corrosion. Considerable research effort has been done to evaluate corrosion effects. It has been found that, corrosion causes reduction of steel properties (Cairns et al 2005), losses of bond between concrete and steel rebars, cracking, and spalling of concrete cover (Li et al 2006). Another factor of great importance is live load growth with time. Additional resistance through strengthening technique is required to compensate for losses in section resistance. Recently, carbon fibre reinforced plastic CFRP materials have used for the purpose of strengthening; laminates are externally bonded to the concrete tensile surface to produce additional bending or shear strength. In the last two decades, the flexural behaviour of CFRP strengthened RC beams has been studied in a significant number of studies. Different failure modes were observed, which can be classified in two types according to location. First, failure modes occur at position of maximum moment. Such modes are concrete crushing, CFRP mid span debonding, and CFRP rupture. Second, failure modes occur at plate ends. Herein, failure modes of the second type were neglected as they can be prevented using anchorage systems. In an early study proposed by Plevris et al (1995), the authors suggested a specific reduction factor (ψCFRP ≈ 0.8) for the CFRP contribution
spread in concrete which is assumed to be relatively moist. 1D Fick’s second law is chosen to represent the diffusion process:
∂ ∂
=
∂ ∂
D C
xcl
2 (1)
where, C is the chloride ion concentration at a depth x in the concrete in the diffusion direction, t is the time and Dcl is the chloride diffusion coefficient in concrete which is taken as:
D D f T f t f Rcl cl ref cl cl, ) ) )H1 2 3cl (2)
where Dcl,ref is a value of Dcl which corresponds to a reference temperature (Tref = 298 K), at a critical relative humidity (RHc = 0.75), and at a reference time (tref = 28 days). The three functions in (Eq. 2) were formulated by Val & Trapper (2008) as:
f T Ucl c rT ef1 1) exp[ ( /1 / )T / ]R= (3a)
f t tcl ref mage
2 ) ( /t )= (3b)
f R RHcl C3 4 4 11)H [ (1 ) /( )RH ]− (3c)
where, T is the absolute temperature in (Kelvin), Uc (=44.6 ± 4.46 kJ/mol) is the activation energy, R is the universal gas constant, mage is the aging coefficient, and RH is the relative humidity. Dcl,ref is influenced by mix proportions, curing, compaction … etc, and can be expressed as (Vu & Stewart 2000):
D D wc
ac
wc wc
, / .
